Spread spectrum communication system with automatic rate detection

ABSTRACT

A multi-channel direct sequence spread-spectrum communication system with the capability of automatic rate detection consists of a plurality of signal channels and a plurality of data channels. During signaling period, only the signaling channels corresponding to the desired symbol repetition and the data channels corresponding to the highest index among the indexes of all active data channels will be allowed to transmit. During data transmission period, only the active data channels will be allowed to transmit. Receiver will use the information provided in preamble signal and mid-amble signal to obtain the number of symbol repetition, the set of active data channels and etc, and to set up initial synchronization.

BACKGROUND

[0001] A spread spectrum communication system is such a system thattransmission bandwidth is substantially higher than data rate. In adirect sequence spread spectrum communication system, at transmitterside, a data sequence is modulated by a pseudo random chip sequence togenerate spread spectrum signal. Usually the chip rate of the pseudorandom sequence is much higher than the rate of the data sequence,resulting in the spread spectrum signal having significant widerbandwidth than that of the data sequence itself. The spread spectrumsignal is then transmitted over a communication media to a receiver. Atthe receiver side, the received spread spectrum signal is multiplied bya local pseudo random chip sequence to despread and recover thecontained information.

[0002] Having many advantages over other communication systems, directsequence spread spectrum communication system is one of the majorcommunication systems widely used in today's society. However, regulardirect sequence spread spectrum communication system has somedisadvantages. One of the major disadvantages is low spectrumefficiency. Nowadays more and more applications require higher andhigher data rate but the available bandwidth is both very expensive andlimited. The low spectrum efficiency in a regular direct sequence spreadspectrum communication system will greatly restrict its opportunity tobe used in many high data rate applications.

[0003] Multi-channel direct sequence spread spectrum communicationssystem is one of the attempts to increase data rate and therefore toimprove the spectrum efficiency of direct sequence spread spectrumcommunication system. Basically, a multi-channel direct sequence spreadspectrum communication system transmits a set of spreading signalssimultaneously over a given frequency bandwidth.

[0004] Beside high spectrum efficiency, a communication system is alsoexpected to be able to provide different data rates to meet varioustransmission requirements, which are determined by various applicationsand by different transmission environments.

[0005] In today's society, there are many different transmissionapplications such as transmitting voice, sending short text message,making video conference call, downloading files from internet, emailingphotos to friend and watching movie. Usually different applicationrequires different transmission rates. A good communication systemshould be able to provide many different transmission rates to meet therequirements of different applications.

[0006] Different transmission environments also require a communicationsystem, especially a wireless communication system, to have differentdata rates. When transmission condition is good, such as a mobilestation is close to a base station, it may be desirable for acommunication system to transmit message with higher data rate. Whentransmission condition deteriorates, such as a mobile station is faraway from a base station, or there is a serious fading, it may beattractive for a communication system to transmit message with lowerdata rate in order to have reliable communication.

[0007] A multi-channel communication system has the inborn capability tosupport many different data rates. To have different rates, amulti-channel communication system can simply use part of its channelsfor data transmission and prevent the rest channels from transmitting.For example, if only one channel is used for data transmission and therest channels are shut off, then one data rate can be provided. If twochannels are used for data transmission and the rest channels are shutoff, then another data rates can be provided. If symbol repetitions areallowed, more data rates can be provided. The combinations of differentnumber of active channels and different number of symbol repetitions canresult in many different data rates.

[0008] Usually, a receiver is informed the change of data rate by atransmitter through upper layer of protocol, which not only costs thecapacity of a communication system, but also cause overall delay. In apacket-switched communication system, the packet received could comefrom total different source than the previous one and thereforegenerally there is no any relation between two adjacent packets. Whendata rate is high and transmission environment changes rapidly, thedelay could cause a receiver of a packet-switched communication systemhaving no enough time to decode the intended data rate and thereforeunable to correctly demodulate.

[0009] Therefore, there is a need to provide a mechanics for a receiverin a multi-channel direct sequence spread spectrum communication systemto automatically detect the data rate set up by a transmitter.

SUMMARY OF INVENTION

[0010] The primary objective of the invention is to make a multi-channeldirect sequence spread-spectrum communication system to have thecapability to automatically detect the data rates.

[0011] Another objective of the invention is to provide a signalstructure for a preamble signal so that a multi-channel direct sequencecommunication system can detect transmission data rate automatically,search for multi-paths, and make initial synchronization.

[0012] Another objective of the invention is to provide a signalstructure for a mid-amble signal so that a multi-channel direct sequencecommunication system can detect the change of transmission data rateautomatically, update multi-path information, disable weak path, andestablish new strong path.

[0013] Another objective of the invention is to provide method so that amulti-channel direct sequence communication system can be more flexiblein changing transmission data rate without resorting to upper layers norinterrupting communication.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The drawing figures depict preferred embodiments of the presentinvention by way of examples, not by way of limitations. In the figures,like reference numerals refer to the same or similar elements.

[0015]FIG. 1 is a diagram of the transmissions around a preamble signaland a mid-amble signal.

[0016]FIG. 2 is a block diagram schematically showing the configurationof a transmitter of a multi-channel direct sequence spread spectrumcommunication system according to the first embodiment of the invention.

[0017]FIG. 3 is a block diagram schematically showing the configurationof a receiver of a multi-channel direct sequence spread spectrumcommunication system according to the first embodiment of the invention.

[0018]FIG. 4 is a block diagram schematically showing the configurationof a transmitter of a multi-channel direct sequence spread spectrumcommunication system according to the second embodiment of theinvention.

[0019]FIG. 5 is a block diagram schematically showing the configurationof a receiver of a multi-channel direct sequence spread spectrumcommunication system according to the second embodiment of theinvention.

DETAILED DESCRIPTION OF THE PREFFERED EMBODIMENTS

[0020] Detailed description of the preferred embodiments is providedherein. The embodiments illustrate multi-channel direct sequence spreadspectrum communication systems with the capability to automaticallydetect transmission data rates. However, it is to be understood that thepresent invention may be embodied in many different ways. For thoseskilled in the art, it could be easy to modify the embodiments. Forexample, instead of using a 16-ary phase-shift keying (PSK) phasemapping device, one can use a mapping device related to M-ary PSK, M-aryquadrature amplitude modulation (QAM) or M-ary pulse amplitudemodulation (PAM). Therefore, specific details disclosed are not to beinterpreted as limitations, but rather as bases for the claims and asrepresentative bases for teaching one to employ the present invention invirtually any appropriately detailed system, structure or manner.

[0021] The top diagram in FIG. 1 shows the beginning of a transmission.At the beginning of each transmission, there are L symbol periodsA_(i),i=1, . . . , L dedicated for setting up AGC. The number L shouldbe big enough so that when the received signal strength is in designrange, in L symbol periods, the receiving amplifier should bring theamplified signal into operational range. Immediately after the L symbolperiods, there are M symbol periods H_(J), j=1, . . . , M dedicated forsignaling. The signal transmitted during these M symbol periods can beused not only to detect the intended transmission rate, but also tosearch for multi-paths and to build initial synchronization. After the Msymbol periods, there are many symbol periods I_(k), k=1, . . . ,dedicated for data transmission.

[0022] The bottom diagram in FIG. 1 shows the conjunction between twotransmissions. There are N symbol periods J_(k), k=1, . . . , Ndedicated for a previous data transmission. After the N symbol periods,there are M symbol periods H_(J), j=1, . . . , M dedicated forsignaling. Also the signal transmitted during these M symbol periods canbe used not only to detect the new transmission rate, but also to updatethe information about multi-paths and to set up initial synchronizationfor new links. The transmission data rate provided in these M symbolperiods makes a communication system be able to change the transmissiondata rate without interrupting communication nor resorting to upperlayers of a protocol. After the M symbol periods, there are many symbolperiods I_(k), k=1, . . . , dedicated for data transmission.

[0023] The number M should be big enough so that the energy accumulatedthrough M symbol periods on each active channel is equal to or largerthan the energy accumulated by each of the active data channels duringnormal data transmission.

[0024] For easy to describe, it may be worthwhile to define some terms.Any of these L symbol periods for setting up AGC is called an AGC periodand any of these M symbol periods for signaling is called a signalingperiod. If the signal generated by various channels during these Msignaling periods is around the beginning of a transmission, the signalwill be called preamble signal. If the signal generated by variouschannels during these M signaling periods is between two transmissions,it will be called mid-amble signal. Any symbol period represented byI_(k) or J_(k) is called a data period.

[0025] More terms can be defined for simplicity. A symbol transmitted bya channel in an AGC period is called an AGC symbol and the symbolstransmitted by all active channels in an AGC period is called amulti-channel AGC symbol. Similarly, a symbol transmitted by a channelin a signaling period is called a signaling symbol and the symbolstransmitted by all active channels in a signaling period is called amulti-channel signaling symbol. Further, a signaling symbol generated bya signaling channel is called a dedicated signaling symbol. In a similarway, a symbol transmitted by a channel in a data period is called a datasymbol and the symbols transmitted by all active channels in a dataperiod is called a multi-channel data symbol. The symbols transmitted byall active channels in a symbol period are called a multi-channelsymbol.

[0026]FIG. 2 illustrates a transmitter of a multi-channel directsequence spread-spectrum communications system according to the firstembodiment of the invention. Before describing the function of eachcomponent, it may be helpful to have an overall picture first.

[0027] There are 64 spreading codes denoted by C₁ to C₆₄ and there are64 channels each corresponding to one of the 64 spreading codes. Thechannels corresponding to spreading codes C₅₇ to C₆₄ are only used forsignaling and called signaling channel for these channels will be shutoff during normal data transmission. The channels corresponding tospreading codes C₁ to C₅₆ are called data channels because thesechannels are mainly for data transmission even they may be used forsetting up AGC and assisting signaling.

[0028] The channel corresponding to spreading code C₁ is called channeli , where 1≦i≦64.

[0029] The transmitter can transmit with its maximum transmission rateat 224 bits per symbol period when all of the 56 data channels are usedfor data transmission and when there is no symbol repetition intransmission. If there are some symbol repetitions, or if only part ofthe 56 data channels will be used for transmission, then a fraction ofthe maximum transmission rate is possible and therefore provides manydifferent transmission rates.

[0030] A switch controls whether a channel is on or off. There is aswitch with each of the 64 channels. When a switch is close, the signalgenerated by the corresponding channel is sent to the complex signalcombiner 225 and therefore the channel is on. When the switch is open,the signal generated by the corresponding channel is not sent to thecomplex signal combiner 225 and therefore the channel is off.

[0031] A multi-channel AGC symbol could be any multi-channel symbol aslong as the multi-channel AGC symbol is not identical to any of thepossible multi-channel signaling symbols and any of the possiblemulti-channel data symbols. In this example, one can take the symbolsgenerated by all 64 channels in a symbol period as a multi-channel AGCsymbol.

[0032] A multi-channel signaling symbol consists of symbols generated byat least one of the 8 signaling channels and exactly one symbol from oneof the 56 data channels.

[0033] A different number of symbol transmissions is assigned to each ofthe 8 dedicated signaling symbols. For example, one can assign 2⁰=1transmission to the dedicated signaling symbol generated by channel 57,2 ¹=2 transmissions to the dedicated signaling symbol generated bychannel 58, 2 ²=4 transmissions to the dedicated signaling symbolgenerated by channel 59, . . . , and 2⁷=128 transmissions to thededicated signaling symbol generated by channel 64. The combinations of8 dedicated signaling symbols can provided 2⁸−1=255 differenttransmissions. For example, when channel₅₇, channel₅₈ and channel₅₉ areon and the rest signaling channels are off, then each of the datasymbols will be transmitted 2⁰+2¹+2²=7 times.

[0034] During signaling periods, one and only one of the data channelsis on. If a particular data channel is on during signaling periods, thenall the data channels whose channel index are smaller than the index ofthat particular channel will be on during normal data transmission. Forexample, during signaling period, among the 56 data channels, if onlychannel 15 is on, then during normal data transmission, the channel 1 tochannel 15 will be used to transmit data.

[0035] The combinations of 8 signaling channels and the selections of 56data channels can provide 255×56=14,280 different transmission modes.

[0036] After signaling period, a series of multi-channel data symbolswill be transmitted. A multi-channel data symbol is the combination ofsymbols generated by each of the active data channels.

[0037] Now it is time for detail description of each element in FIG. 2.

[0038] The switch S_(A) is connected to 224 bits with each bit set to 0during AGC period and signaling period. During data transmission period,the switch S_(A) is connected to the input data bus 205. The 224 databits on bus 205, through switch S_(A), are separated into 56 groups witheach group having 4 bits. In case only part of 56 channels will be usedfor transmission, the bits corresponding to the inactive channels can befilled with bit 0. Each group of 4 bits is fed to one of the 56 16-aryPSK phase mapping devices labeled as 210 ₁ to 210 ₅₆. There are 8 16-aryPSK phase mapping devices corresponding to 8 signaling channels. Each ofthe 8 16-ary PSK phase mapping devices has 4 bits 0000 as its input.

[0039] A 16-ary PSK phase mapping device maps its 4-bit input into acomplex number corresponding the one of the 16 phases. The output ofeach of the 64 16-ary PSK phase mapping devices will be multiplied by acorresponding spreading code from C₁ to C₆₄at the multipliers 215 ₁ to215 ₆₄ respectively. When a particular channel is used, thecorresponding switch will close. Each of the 64 switches S₁, to S₆₄ willdetermine if the output of a corresponding multiplier will be fed to acomplex signal combiner device 220. All the signals fed to complexsignal combiner device 220 will be summed up.

[0040] The output of complex signal combiner 220 is separated into realsignal I and imagery signal Q. The I and Q signals are scaled by scalers225 _(I) and 225 _(Q), to obtain the scaled I and Q signalsrespectively. The purpose of the scalers 225 _(I) and 225 _(Q) is tomake proper scaling so that the transmitting power will be not changedwith different number of active channels. Usually the scalers 225 _(I)and 225 _(Q) have identical gains.

[0041] The scaled I signal is multiplied by a PN code or a scramble codeor a cover code at multiplier 230 _(I) and then is converted into ananalog signal by a digital to analog converter (DAC) 235 _(I). Theconverted I signal is further modulated by cos(ωt) at multiplier 240_(I). Similarly, The scaled Q signal is multiplied by the same PN codeor the same scramble code or the same cover code at multiplier 230 _(Q)and then is converted into an analog signal by another digital to analogconverter (DAC) 235 _(Q). The converted Q signal is further modulated bysin(ωt) at multiplier 240 _(Q). The signals from both I and Q paths arecoupled together and go through a power amplifier 245 and then throughantenna 250 to transmit.

[0042]FIG. 3 illustrates a receiver of a multi-channel direct sequencespread-spectrum communications system according to the first embodimentof the invention.

[0043] The signal enters the receiving antenna 305 and goes through again controllable amplifier 310. There are cos(ωt) and sin(ωt) from theoutputs of voltage controlled oscillator (VCO) 315. The signal from thegain controllable amplifier 310 is multiplied at multiplier 320 _(I) bycos(ωt) and multiplied at multiplier 320 _(Q) by sin(ωt). The outputs ofmultiplier 320 _(I) and multiplier 320 _(Q) are fed to analog to digitalconverters (ADC) 325 _(I) and 325 _(Q) to obtain digital I and Q signalsrespectively.

[0044] Both the digital I and Q signals from outputs of analog todigital converters 325 _(I) and 325 _(Q) are sent to dynamic matchedfilter bank 335, which also takes the spreading codes C₁ to C₆₄ and thePN code generated by PN generator 330 as its inputs.

[0045] When each of the reference signals at any symbol period isidentical to the signal at its previous period, a group of regularmatched filters, or a regular matched filter bank, can be used to findhow closely the received signal matches to each of the referencesignals. However, when at least one of the reference signals at somesymbol period is not identical to the signal at its pervious symbolperiod, then a dynamic matched filter bank is used to find how closelythe received signal matches to each of the reference signals. In theexample given by FIG. 2, if the period of the PN signal is longer than asymbol period, then the reference signals consisting of 64 spreadingcodes scrambled by the PN signal do change over each symbol period andtherefore, a dynamic matched filter bank should be used.

[0046] There are 64 outputs from dynamic matched filter bank 335 witheach output being a signal of a complex number. During AGC period andsignal period, all the output will be sent to controller and informationextractor 350. The purpose of 350 is to find the information such as theset of active data channels and symbol repetition contained in thesignaling symbols. The phase information contained in a preamble signalor mid-amble signal can be used for initialize a rake structure,generate initial synchronization, and generate various control signals.

[0047] The outputs of dynamic matched filter bank 335, with index 1 to56, will sent to accumulators 340 ₁ to 340 ₅₆ respectively and will beaccumulated a fixed number of times determined by the informationextracted from multi-channel signaling symbols by 350. The output ofaccumulators 340 ₁ to 340 ₅₆ will be sent to 56 16-ary PSK decoders 345₁ to 345 ₅₆ to decode. The bit combiner 355 will merge all the bits fromthe 56 16-ary PSK decoders 345 ₁ to 345 ₅₆ together.

[0048]FIG. 4 illustrates a transmitter of a multi-channel directsequence spread-spectrum communications system according to the secondembodiment of the invention.

[0049] The transmitter in FIG. 4 is similar to the transmitter in FIG. 2and a device in FIG. 4 is just like the corresponding device in FIG. 2.The difference between FIG. 4 and FIG. 2 is that in FIG. 4, the inputdata bus 405 has 256 bits instead of 224 bits, and through switch S_(A),is divided into 64 groups instead of 56 groups. Each of the 64 groups isconnected to a corresponding channel from channel 1 to channel 64.

[0050] Again assume that C₁ to C₅₆ are the 8 signaling channels. Inorder to support higher data rate, the 8 signaling channels will be alsoused for data transmission and therefore they are data channels. Whenthere are less than 56 active data channels, one can construct signalingsymbol just in the way described before. When there is a need for morethan 56 active channels, one can further request that no symbolrepetition is allowed and during signaling periods, the only activechannel is the channel having the highest index among all active datachannels. For example, in order to have 60 active data channels, for 60is larger than 56, one could set channel 60 active and shut off the restchannels during signaling periods and transmit channel 1 to channel 60during data periods.

[0051] In order to have a multi-channels AGC symbol being different fromeither any of multi-channel signaling symbols or any of themulti-channel data symbols, a multi-channels AGC symbol could be themulti-channel symbols generated by all the channels except channel 1.

[0052]FIG. 5 illustrates the receiver of a multi-channel direct sequencespread-spectrum communications system according to the second embodimentof the invention. It is corresponding to the transmitter in FIG. 4. Adevice is FIG. 5 is just like the corresponding device in FIG. 3. Theonly difference is that instead of having just 56 accumulators and 5616-ary PSK decoders as in FIG. 3, there are 64 accumulators and 6416-ary PSK decoders. Also the bit combiner has an output of 256 bitsinstead of 224 bits.

What is claimed as:
 1. A multi-channel direct sequence spread-spectrumcommunication system, comprising: a bit separator for separating a blockof data bits into a plurality of sub-blocks of data bits with eachsub-block corresponding to a respective channel; a plurality ofsubmodulators, wherein a respective submodulator receives acorresponding sub-block from the bit separator, maps the sub-block intoa signal, and modulates the signal with the corresponding spreadingcode; a plurality of switches, wherein a respective switch is forturning on and shutting off a corresponding channel; a signal combinerfor algebraically combining the plurality of direct sequence spreadspectrum signals from each of the active channels to form amulti-channel direct sequence spread spectrum signal; a detection devicefor projecting the received multi-channel direct sequence spreadspectrum signal on each of the spreading codes; an information extractorfor finding information such as the set of active channels and thenumber of symbol repetition from signaling symbols; a controller forgenerating control signals for various devices in the system; aplurality of accumulators for integrating the signal energy for each ofthe data channels; a plurality of subdemodulators for demodulatingsignal from the direct sequence spread spectrum signal projected on eachchannel; and a bit combiner for combining sub-blocks each from acorresponding subdemodulator to form a big block of bits.
 2. Amulti-channel spread-spectrum communication system as in claim 1,wherein each of submodulators comprises an M-ary phase mapping circuitfor mapping a corresponding sub-block into a complex number representingone of the M-ary phases and a multiplier multiplying the complex numberwith a corresponding spreading code.
 3. A multi-channel spread-spectrumcommunication system as in claim 1, wherein each of submodulatorscomprises an M-ary QAM mapping circuit for mapping a correspondingsub-block into a complex number representing one of the M-ary QAMsignals and a multiplier multiplying the complex number with acorresponding spreading code.
 4. A multi-channel spread-spectrum systemcommunication as in claim 1, wherein each of submodulators comprisesM-ary PAM mapping circuit for mapping a corresponding sub-block into anumber representing one of the M-ary PAM signals and a multipliermultiplying the number with a corresponding spreading code.
 5. Amulti-channel spread spectrum communication system as in claim 1,wherein a detection device comprises a plurality of correlators witheach correlator is for obtaining the correlation between the receivedmulti-channel direct sequence spread spectrum signal and thecorresponding spreading code scrambled by a PN code.
 6. A multi-channelspread-spectrum communication system as in claim 1, wherein a detectiondevice comprises a plurality of matched filters with each filter is forobtaining the correlation between the received multi-channel directsequence spread spectrum signal and the corresponding spreading codescrambled by a PN code.
 7. A multi-channel spread-spectrum communicationsystem as in claim 1, wherein each of subdemodulators comprises an M-aryPSK demodulator for obtaining the phase signal from the multi-channeldirect sequence spread spectrum signal projected on the correspondingchannel and reverse mapping the phase into a sub-block of bits.
 8. Amulti-channel spread-spectrum communication system as in claim 1,wherein each of subdemodulators comprises an M-ary QAM demodulator forobtaining the information-bearing real and imaginary magnitudes from themulti-channel direct sequence spread spectrum signal projected on thecorresponding channel and reverse mapping the real and imaginarymagnitudes into a sub-block of bits.
 9. A multi-channel spread-spectrumcommunication system as in claim 1, wherein each of subdemodulatorscomprises an M-ary PAM demodulator for obtaining the information-bearingmagnitude from the multi-channel direct sequence spread spectrum signalprojected on the corresponding channel and reverse mapping the magnitudeinto a sub-block of bits.
 10. A multi-channel spread-spectrumcommunication system as in claim 1 further comprises a plurality ofscaling devices for keeping the transmitted power invariable with thenumber of active channels.
 11. A method of automatic data rate detectionfor a multi-channel spread-spectrum communication system, comprising:transmitting signals from each of the representative channels for adesired symbol repetition; transmitting signals from each of therepresentative channels for a group of active data channels; detectingthe number of symbol repetition and the set of active data channels; andgenerating various control signals for controlling corresponding devicesin the system.
 12. A method as in claim 11, wherein the representativechannels for a desired symbol repetition comprises the selected channelsfrom a set of channels with each channel in the set having an assignedsymbol repetition number and a predefined arithmetic operation procedureon the numbers associated with the selected channels will obtain thedesired symbol repetition.
 13. A method as in claim 11, wherein therepresentative channels for a group of active data channels comprisesthe channels which must be on during signal periods whenever the groupof data channels will be active during normal data transmission.
 14. Amethod as in claim 11, further comprises: separating a block of databits into a plurality of respective sub-blocks of data bits; mappingeach of respective sub-block of data bits into an electrical signal; andmodulating each electrical signal with a corresponding spreading code.15. A method as in claim 11, further comprises: projecting the receivedmulti-channel direct sequence spread spectrum signal on each of thescrambled spreading codes; demodulating the information-bearing signalsfrom the multi-channel direct sequence spread spectrum signal projectedon each of the scrambled spreading codes; reverse mapping each of theinformation-bearing signals into a corresponding sub-block of data bits;and merging all the sub-blocks of data bits into a big block of databits.
 16. A multi-channel direct sequence spread spectrum communicationsystem, comprising: a stream separator for dividing an input data streaminto a plurality of data sub-stream signals with each data stream signalcorresponding to a respective channel; a plurality of mapping circuits,wherein a respective mapping circuit is coupled to receive acorresponding data sub-stream signal from the stream separator and mapspredetermined-length segments of the respective data sub-stream signalto a signal of a complex number; a plurality of multipliers, wherein arespective multiplier is for modulating each spreading code with acorresponding signal of a complex number to generate a direct sequencespread spectrum signal for a corresponding channel; a plurality ofswitches, wherein a respective switch is for controlling on and off acorresponding channel; a signal combiner, receiving the direct sequencespread spectrum signals from the switches, for algebraically combiningthe plurality of direct sequence spread spectrum signals from each ofthe active channels to form a multi-channel direct sequence spreadspectrum signal consisting of an in-phase multi-channel direct sequencespread spectrum signal and a quadrature multi-channel spread spectrumsignal; a plurality of scalers for scaling the multi-channel directsequence spread spectrum signal so that the signal strength isinvariable with the number of active channels; and a plurality ofsubdemodulators, wherein a respective subdemodulator is for demodulatingthe corresponding direct sequence spread spectrum signal bore in themulti-channel direct sequence spread spectrum signal to regenerate thedata stream of the corresponding channel.
 17. A multi-channel directsequence spread spectrum communication system as in claim 16, furthercomprising a plurality of sequence modulators for modulating themulti-channel direct sequence spread spectrum signal with a sequencefrom a sequence group consisting of scramble codes, signature codes, andPN codes.
 18. A multi-channel direct sequence spread spectrumcommunication system as in claim 16, further comprising a radiofrequency modulator for modulating the in-phase multi-channel directsequence spread spectrum signal with an in-phase spread spectrum carrierand the quadrature multi-channel spread spectrum signal with aquadrature spread spectrum carrier.
 19. A multi-channel direct sequencespread spectrum communication system as in claim 16, further comprisinga plurality of code detection devices selected from the group consistingof matched filters and correlators.
 20. A multi-channel direct sequencespread spectrum communication system as in claim 16, further comprisinga radio frequency demodulator for demodulating the receivedmulti-channel direct sequence spread spectrum signal with an localin-phase spread spectrum carrier and a local quadrature spread spectrumcarrier.